Acceleration switch

ABSTRACT

An acceleration switch that operates even when acceleration is applied to the acceleration switch from a direction other than a predetermined detection direction. The acceleration switch ( 1 ) includes a movable portion (M 1 ), which has a movable electrode ( 12 ), and a fixed electrode ( 14 ). The movable portion includes an inertial weight ( 8 ) moved in accordance with the application of acceleration, a beam portion ( 10 ) for pivotably supporting the inertial weight, and a plurality flexible plates ( 11 ) that are arranged in the inertial weight and each have a distal end in which the movable electrode is located and are flexed separately from one another. The flexible plates separately move to contact the fixed portion when acceleration is applied from a direction other than a predetermined direction.

FIELD OF THE INVENTION

[0001] The present invention relates to an acceleration switch, and moreparticularly, to an acceleration switch that includes a movable portion,which has a movable electrode, and a fixed electrode and that moves themovable portion when acceleration is applied so that the movableelectrode contacts the fixed electrode.

BACKGROUND ART

[0002] Many automobiles are nowadays equipped with air bag systems. Anair bag system generally includes an air bag, an ignitor, and anelectronic control unit (ECU). The ECU includes an acceleration sensor,which detects a sudden change in acceleration when the vehicle collides.A semiconductor acceleration sensor is used as such type of anacceleration sensor. The semiconductor acceleration sensor includes, forexample, a strain gauge arranged on a beam, which supports a mass. TheECU activates the ignitor when determining that the applied accelerationis greater than or equal to a predetermined value. The thermal expansionof heated air instantaneously inflates a folded air bag.

[0003] The ECU may function erroneously when affected by electromagneticwaves generated by surrounding devices. Therefore, the employment of amechanical acceleration switch (i.e., safing sensor) in addition to anelectronic acceleration sensor has been proposed. The mechanicalacceleration switch is less affected by the electromagnetic waves thanthe electronic acceleration sensor.

[0004]FIGS. 1A to 1C schematically show the structure of a prior artacceleration switch 51.

[0005] The acceleration switch 51 includes a silicon chip 52 and asubstrate 53, which are attached to each other. The silicon chip 52 hasa hollow portion 52 a, in which a generally rectangular parallelepipedinertial weight 54 is arranged. A beam 55 is provided on each long sideof the inertial weight 54 at a position offset from the middle of thelong side. The beams 55 connect the inertial weight 54 and the siliconchip 52. The beams 55 support the inertial weight 54 at a positionoffset from the center (center of gravity) of the inertial weight 54.Two movable electrodes 56, 57 are arranged close to each other on thelower surface of the inertial weight 54 at a generally middle part ofthe distal end that is on the side farther from the beams 55.

[0006] A hollow portion 53 a is defined in the upper surface of thesubstrate 53. A fixed electrode 58 is arranged in the hollow portion 53a at a position corresponding to the movable electrodes, 56, 57. Themovable electrodes 56, 57 are normally spaced from the fixed electrode58.

[0007] When acceleration is applied to the acceleration switch 51,inertial force is applied to the inertial weight 54 such that theinertial weight 54 pivots about the beam 55 in a downward direction (thedirection indicated by arrow G in FIG. 1A). When the accelerationapplied to the acceleration switch 51 becomes greater than or equal to apredetermined value, the inertial weight 54 pivots in a directionindicated by arrow F in FIG. 1A, and the movable electrodes 56, 57contact the fixed electrode 58. When the acceleration is small, theinertial weight 54 does not pivot about the beam 55. Thus, the fixedelectrode 58 does not contact the movable electrode 56. The accelerationswitch 51 operates only when the applied acceleration is greater than orequal to the predetermined value.

[0008] When acceleration is applied to the acceleration switch 51 from adirection other than a predetermined detection direction, inertial forceis applied to the inertial weight 54 from a direction indicated by arrowG in FIG. 2A. In such case, the inertial weight 54 pivots in a twistedstate, as shown in FIG. 2A. In such state, an edge of the lower surfaceof the inertial weight 54 first contacts the substrate 53, as shown inFIG. 2B. This restricts the movement of the inertial weight 54. The twomovable electrodes 56, 57, which are on the same plane, may not contactthe fixed electrode 58. In other words, contact failure may occur in theacceleration switch 51 when acceleration is applied from a directionother than the predetermined detection direction.

DISCLOSURE OF THE INVENTION

[0009] It is an objective of the present invention to provide anacceleration switch, which operation is guaranteed even whenacceleration is applied to the acceleration switch from direction otherthan the a predetermined detection direction.

[0010] One perspective of the present invention provides an accelerationswitch including a movable portion, which has a movable electrode, and afixed electrode, in which movement of the movable portion in accordancewith the application of acceleration causes the movable electrode tocontact the fixed electrode. The acceleration switch has the movableportion, which includes an inertial weight moved in accordance with theapplication of acceleration, a beam portion for pivotably supporting theinertial weight, and a plurality of flexible plates arranged in theinertial weight, each of which has distal end, in which the movableelectrode is located, and is flexed separately from one another.

[0011] In this structure, since the plurality of flexible plates, eachprovided with the movable electrode, flex separately, the movableelectrodes move separately when the flexible plate are flexed.Therefore, even if only one of the movable electrodes contacts the fixedelectrode when acceleration is applied to the acceleration switch froman unexpected direction, the other movable electrode moves separatelyfrom the former movable electrode and contacts the fixed electrode.Therefore, the activation of the acceleration switch is guaranteed evenwhen acceleration is applied from an unexpected direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention, together with objects and advantages thereof, maybest be understood by reference to the following description of thepresently preferred embodiments together with the accompanying drawingsas described below.

[0013]FIG. 1A is a schematic cross-sectional view of a prior artacceleration switch

[0014]FIG. 1B is a schematic bottom view of a silicon chip configuringthe acceleration switch of FIG. 1A.

[0015]FIG. 1C is a cross-sectional view taken along line A-A in FIG. 1B.

[0016]FIGS. 2A and 2B are schematic enlarged views showing the movementof a movable portion when acceleration is applied to the prior artacceleration switch from an unexpected direction.

[0017]FIG. 3A is a schematic cross-sectional view of an accelerationswitch according to one embodiment of the present invention.

[0018]FIG. 3B is a schematic bottom view of a silicon chip configuringthe acceleration switch of FIG. 3.

[0019]FIG. 3C is a cross-sectional view taken along line A-A in FIG. 3B.

[0020]FIG. 4A is a schematic plan view of the silicon chip illustratinga procedure for manufacturing the acceleration switch of FIG. 3A.

[0021]FIG. 4B is a cross-sectional view taken along line B-B in FIG. 4A.

[0022]FIG. 4C is a cross-sectional view taken along line C-C in FIG. 4A.

[0023]FIG. 5A is a schematic plan view of the silicon chip illustratinga procedure for manufacturing the acceleration switch of FIG. 3A.

[0024]FIG. 5B is a cross-sectional view taken along line B-B in FIG. 5A.

[0025]FIG. 5C is a cross-sectional view taken along line C-C in FIG. 5A.

[0026]FIG. 6A is a schematic plan view of the silicon chip illustratinga procedure for manufacturing the acceleration switch of FIG. 3A.

[0027]FIG. 6B is a cross-sectional view taken along line B-B in FIG. 6A.

[0028]FIG. 6C is a cross-sectional view taken along line C-C in FIG. 6A.

[0029]FIG. 7A is a schematic plan view of the silicon chip illustratinga procedure for manufacturing the acceleration switch of FIG. 3A.

[0030]FIG. 7B is a cross-sectional view taken along line B-B in FIG. 7A.

[0031]FIG. 7C is a cross-sectional view taken along line C-C in FIG. 7A.

[0032]FIG. 8 is a schematic cross-sectional view showing a state inwhich acceleration is applied to the acceleration switch of FIG. 3A.

[0033]FIG. 9 is a schematic cross-sectional view showing a state inwhich acceleration is applied to the acceleration switch in FIG. 3A froman unexpected direction.

[0034]FIGS. 10A to 10C are schematic enlarged views showing the movementof a movable portion in a state in which acceleration is applied to theacceleration switch in FIG. 3A from an unexpected direction.

[0035]FIGS. 11A and 11B are enlarged views schematically showing themovement of a movable portion when acceleration is applied to theacceleration switch of FIG. 3A from an unexpected direction.

[0036]FIGS. 12A to 12C are schematic bottom views of a silicon chip ofan acceleration switch according to further embodiments.

BEST MODE FOR CARRYING OUT THE INVENTION

[0037]FIG. 3A is a schematic cross-sectional view of an accelerationswitch 1 according to one embodiment of the present invention. As shownin FIG. 3A, the acceleration switch 1 is formed by attaching a substrate3 and a silicon chip 2 to each other.

[0038] The silicon chip 2 includes a chip body 4 and a double-layerstructure of epitaxial growth layers 5, 6. The chip body 4 is formedfrom parallelepiped and formed from p-type monocrystal silicon of (110)orientation. The epitaxial growth layers 5, 6 are superimposed on oneside of the chip body 4 and formed from n-type monocrystal silicon. Thethickness of the chip body 4 is 500 μm to 600 μm. The thickness of eachof the epitaxial growth layers 5, 6 is about 15 μm and, the thickness ofthe two epitaxial growth layers 5, 6 is about 30 μm. To facilitateillustration, the thickness of the epitaxial growth layers 5, 6 isillustrated thicker than actual. A rectangular hollow portion 7 isdefined in the bottom side of the chip body 4. The hollow portion 7 hasa depth of about 100 μm and is thus deeper than the thickness of the twoepitaxial growth layers 5, 6. The hollow portion 7 accommodates amovable portion M1, which includes an inertial weight 8, a balancer 9, abeam portion, or beam 10, and a plurality of (two in the presentembodiment) flexible plates 11.

[0039] The inertial weight 8 and the balancer 9 are rectangular and eachhave a thickness of about 20 μm. The inertial weight 8 is larger andheavier than the balancer 9. The beam 10 is generally cross-like whenseen from above and formed between the inertial weight 8 and thebalancer 9. The beam 10 has a thickness of about 7.5 μm and is flexible.The beam 10 has a set of two opposing ends facing each other, which areconnected to the chip body 4, and another set of two opposing ends,which are connected to one side of the inertial weight 8 and one side ofthe balancer 9. The inertial weight 8 and the balancer 9 are supportedby the beam 10 and are pivotal about the beam 10.

[0040] The two flexible plates 11 are formed integrally with theinertial weight 8 at the side of the beam 10 that is opposite to theside connected to the inertial weight 8. The flexible plates 11 are eacharranged on the distal end of the inertial weight 8 and spaced from thebeam 10. The flexible plates 11 are each trapezoidal when seen fromabove and become narrower from the proximal end toward the distal end.The thickness of each flexible plate 11 is about 7.5 μm, which is aboutthe same as the thickness of the beam 10. The flexible plates 11 areeach formed at the generally middle part of the side of the inertialweight 8. The lower surface of the flexible plates 11 is flush withlower surface of the inertial weight 8.

[0041] The flexible plates are formed close to each other. Morespecifically, the gap between the flexible plates 11 is about 10 μm to200 μm. In the present embodiment, the gap is about 40 μm. A movableelectrode 12 is arranged on the distal end of the lower surface of eachflexible plate 11. The width of each movable electrode 12 is the same asthe width of the distal end of each flexible plate 11. The movableelectrodes 12 are each connected to an external terminal, which is notshown, by a wiring pattern 12 a, which is formed on the flexible plates11, the inertial weight 8, and the beam 10.

[0042] The substrate 3 is rectangular and has the same shape as thesilicon chip 2. In the present embodiment, a glass substrate is used asthe insulative substrate 3. Alternatively, for example, a siliconsubstrate may be used. A rectangular hollow portion 13 is defined in theinner surface of the substrate 3. The hollow portion 13 is formed at aposition corresponding to the hollow portion 7 of the silicon chip 2through, for example, etching. The substrate 3 and the silicon chip 2are bond to each other using a known anode bonding technique. However,the substrate 3 and the silicon chip 2 may be, for example, adhered toeach other with an adhesive instead of using the anode bondingtechnique.

[0043] A fixed electrode 14 is formed in the inner surface of the hollowportion 13 at a position corresponding to the movable electrodes 12.Thus, the movable electrodes 12 contact the fixed electrode 14 when theinertial weight 8 pivots and the flexible plates 11 incline toward thesubstrate 3. In this state, the movable electrodes 12 are electricallyconnected by the fixed electrode 14.

[0044] An example of a procedure for manufacturing the accelerationswitch 1 of the present embodiment using a surface micro-machiningtechnique will now be described with reference to FIGS. 4 to 7.

[0045] The substrate 3 used in the acceleration switch 1 is manufacturedas follows. First, a rectangular glass substrate (e.g., Pyrex glass) isetched to form a hollow portion 13 having a predetermined shape at oneposition in the inner surface of the substrate 3. Then, after maskingthe glass substrate, conductive metal (e.g., aluminum Al) is sputteredto form the fixed electrode 14 in the inner surface of the hollowportion 13. In lieu of a dry film forming process, such as sputtering, awet film forming process such as electroless plating may be employed.

[0046] The manufacturing procedure of the silicon chip 2 will now bedescribed. First, a mask, which is not shown, is applied to the topsurface of a chip body 4. The chip body 4 is then photoetched to form anopening in a predetermined area of the mask. Then, the surface of thechip body 4 undergoes an ion implantation process to implant apredetermined concentration of p-type impurities, such as boron. Thep-type impurities are then thermally diffused. This forms a first highconcentration p-type silicon layer (lower p⁺ silicon implantation layer)21 (see FIG. 4) in the predetermined portion of the silicon chip 2. Theportion in which the lower p⁺ silicon implantation layer 21 is formedcorresponds to where the hollow portion 7 will be subsequently formed.

[0047] Vapor phase growth causes the first epitaxial growth layer 5,which is made of n-type monocrystal silicon, to be formed on the entiretop surface of the chip body 4 on which the p⁺ silicon implantationlayer 21 has been applied. As a result, the p⁺ silicon implantationlayer 21 is implanted in the first epitaxial growth layer 5 (see FIG.4). Then, a mask, which is not shown, is applied to the first epitaxialgrowth layer 5 and photoetched to form an opening at a predeterminedarea of the mask. In this state, for example, ion implantation isperformed to implant p-type impurities. The implanted p-type impuritiesare then thermally diffused. This forms a second high concentrationp-type silicon layer (upper p⁺ silicon implantation layer) 22 in thefirst epitaxial growth layer 5. The upper p⁺ silicon implantation layer22 extends to the lower p⁺ silicon implantation layer 21, which hasalready been formed. The portion in which the upper p⁺ siliconimplantation layer 22 is formed also corresponds to the area where thehollow portion 7 will be formed later. The portion that is masked whenforming the upper p⁺ silicon implantation layer 22 corresponds to a sideof an area, in which the inertial weight 8 and the balancer 9 will besubsequently formed.

[0048] Subsequently, vapor phase growth causes the second epitaxialgrowth layer 6, which is made of n-type monocrystal silicon, to beformed on the entire top surface of the first epitaxial growth layer 5.As a result, the upper p⁺ silicon implantation layer 22 is implanted inthe second epitaxial growth layer 6 (see FIG. 4). Then, a mask (notshown) is applied to the second epitaxial growth layer 6 and photoetchedto form openings at predetermined portions. The implantation ofimpurities and thermal diffusion are performed on p-type impurities. Thep-type impurities are thermally diffused. This forms a third highconcentration p-type silicon layer (p⁺ silicon diffusion layer) 23 inthe first and second epitaxial growth layers 5, 6 (see FIG. 5). The p⁺silicon diffusion layer 23 extends to the upper p⁺ silicon implantationlayer 22. The portions in which the third high concentration p-typesilicon layer (p⁺ silicon diffusion layer) 23 is formed correspond to aportion, in which the hollow portion 7 will subsequently be formed. Theportions that are masked when forming the p⁺ silicon diffusion layer 23correspond to areas in which the inertial weight 8, the balancer 9, thebeams 10, and the flexible plates 11 are formed. In other words, the p⁺silicon diffusion layer 23 is formed to leave space for forming theinertial weight 8, the balancer 9, the beam 10, and the flexible plates11.

[0049] After the high concentration p-type silicon layer forming processis completed, the silicon chip 2 is heated in the presence of oxygen orin the air to form an oxidation film, which is not shown, on the top andbottom surfaces of the silicon chip 2. In this state, Al is sputtered orvapor deposited on the oxidation film. Then, photolithography isperformed. This forms the movable electrodes 12 and the wiring pattern12 a on the surface of areas where the inertial weight 8 and theflexible plates 11 will be formed later.

[0050] Subsequently, sputtering or vapor deposition of, for example,tungsten (W) or molybdenum (Mo) is performed on the silicon chip 2. Thesilicon chip 2 also undergoes photolithography to form a metalprotection film (not shown) having openings. Afterward, the oxidationfilm is removed from portions corresponding to the openings of the metalprotection film to expose the upper surface of the p⁺ silicon diffusionlayer 23, which is hidden under the film. W and Mo are selected becausethese metals resist hydrofluoric acid.

[0051] After the masking process is completed, the silicon chip 2undergoes an anode conversion process as described below.

[0052] A high concentration hydrofluoric acid (HF) solution, which is ananode conversion acid solution, is filled in an anode conversiontreatment tank. Counter electrodes, which are formed from, for example,platinum, and the silicon chip 2, which is faced toward the counterelectrodes, are immersed in the hydrofluoric acid solution. An anode ofa direct current power supply is connected to the rear surface of thesilicon chip 2 while a cathode of the direct current power supply isconnected to the counter electrodes. Thus, direct current flows from theback surface to the upper surface of the silicon chip 2. This results inthe portions formed from high concentration p-type silicon in thesilicon chip 2 (i.e., p⁺ silicon implantation layers 21, 22 and the p⁺silicon diffusion layer 23) becoming selectively porous. Therefore, thefirst to third high concentration p-type silicon layers 21, 22, 23 arereformed into porous silicon layers in the block.

[0053] Subsequent to the anode conversion process and prior to theremoval of the metal protection film, alkali etching is performed.

[0054] A substance such as tetramethylammonium hydroxide (TMAH) is usedas the etchant. The etching dissolves the porous silicon layers. Theporous silicon layer, which defines a reformed portion, is easilydissolved by alkali in comparison to a densified silicon layer, whichdefines a non-reformed portion. Thus, the porous silicon layers areeasily hollowed out to form the hollow portion 7. This also forms themovable portion M1 in the hollow portion 7 (see FIGS. 7). The siliconchip 2 is then reversed and attached to the substrate 3. This completesthe acceleration switch 1 of FIG. 3.

[0055] The operation of the acceleration switch 1 will now be described.Referring to FIG. 8, when acceleration is applied to the accelerationswitch 1, inertial force is applied to the movable portion M1 in thedirection of arrow G. When the acceleration applied to the accelerationswitch 1 becomes greater than or equal to a predetermined value, theinertial weight 8 pivots downwardly about the beams 10, as shown byarrow F in FIG. 8. In this state, inertial force is applied to thebalancer 9 in the same manner. However, the inertial weight 8 is heavierthan the balancer 9 in the mass. Thus, the inertial weight pivotsdownwardly. The two movable electrodes 12 contact the fixed electrode14, and the two movable electrodes are electrically connected(activated) by the fixed electrode 14.

[0056] On the other hand, when acceleration smaller than thepredetermined value is applied to the acceleration switch 1, theinertial weight 8 does not pivot about the beams 10. Therefore, even ifthe beam 10 has some flexibility, the inertial weight 8 avoids moving toa predetermined position. This prevents the both movable electrodes 12from being electrically connected. That is, the acceleration switch 1 isactivated only when acceleration applied to the acceleration switchbecomes greater than or equal to the predetermined value.

[0057] Acceleration may be applied to the acceleration switch 1 from adirection other than a predetermined detection direction (unexpecteddirection). Referring to FIG. 10, a direction of inertial force isindicated by arrow G when acceleration is applied from an unexpecteddirection. The inertial weight 8 twists and pivots when acceleration isgreater than or equal to the predetermined value, as shown in FIG. 10.The operation of the acceleration switch 1 when acceleration is appliedfrom an unexpected direction, will now be described with reference toFIGS. 10 and 11.

[0058] A twisting force is applied to the beam 10 when inertial forcegreater than or equal to the predetermined value is applied to theinertial weight 8 from an unexpected direction, as shown by arrow G inFIG. 10A. Accordingly, the twisted inertial weight 8 starts to pivotdownwardly, as shown in FIG. 10B. Since each flexible plate 11 issufficiently thin as compared with the inertial weight 8, the inertialforce applied to each flexible plate 11 due to acceleration is small.Therefore, the inertial force is applied substantially only to theinertial weight 8. The flexible plates 11 do not bend about the portionconnected with the inertial weight 8 when acceleration is applied.Therefore, each flexible plate 11 pivots integrally with the inertialweight 8.

[0059] One of the movable electrodes 12 contacts the fixed electrode 14as the inertial weight 8 pivots downwardly, as shown in FIG. 10C. Sinceinertial force is still applied to the inertial weight 8 in this state,the inertial weight 8 continuously pivots in a downward direction.Referring to FIG. 11A, further pivoting of the inertial weight 8 causesthe flexible plate 11 contacting the fixed electrode 14 to bend. Sincethe flexible plate 11 is independent from each other, the bendingflexible plate 11 does not influence the other flexible plate 11. Thus,as the inertial weight 8 further pivots downward, one of the flexibleplates 11 downwardly moves while the other flexible plates 11 bend whilekeeping contact with the fixed electrode 14. Accordingly, the movableelectrode 12 of the other flexible plate 11 also contacts the fixedelectrode 14, as shown in FIG. 11B.

[0060] In the switch 1 according to the present embodiment, contact ofthe movable electrodes 12 with the fixed electrode 14 is guaranteed evenif acceleration that is greater than or equal to the predetermined valueis applied to the inertial weight 8 from an unexpected direction.Accordingly, the operation of the acceleration switch 1 is guaranteed.

[0061] The acceleration switch 1 according to the embodiment has thefollowing advantages.

[0062] (1) Since the two flexible plates 11, each provided with themovable electrode 12, elastically flex separately, the movableelectrodes 12 move separately when the flexible plates 11 are flexed.Therefore, even if only one of the movable electrodes 12 contacts thefixed electrode 14 when acceleration is applied to the accelerationswitch 1 from an unexpected direction, the other movable electrode 12moves separately from the former movable electrode 12 and contacts thefixed electrode 14. Accordingly, the activation of the accelerationswitch 1 is guaranteed even when acceleration is applied from anunexpected direction.

[0063] (2) The flexible plates are each thinner than the inertial weight8. This ensures elastic flexing of each flexible plate 11. In addition,the flexible plates are less influenced by inertial force.

[0064] Further, since the thickness of the flexible plates 11 is thesame as that of the beams 10 in the present embodiment, the flexibleplates 11 are formed in the same process as the beams 10 whenmanufacturing the silicon chip 2. Therefore, the number of processes formanufacturing the silicon chip 2 is prevented from increasing.

[0065] (3) The width of the distal end of the flexible plates 11 issubstantially the same as that of the movable electrodes 12. Thisensures that the movable electrodes 12 contact the fixed electrode 14when the flexible electrodes move downwardly in a twisted state.

[0066] (4) The flexible plates 11 are each generally trapezoidal andbecome narrower toward the distal end. This increases the strengthconnecting the flexible plates 11 and the inertial weight 8 to eachother.

[0067] (5) The flexible plates 11 are each formed close to each other.This reduces the time for the movable electrodes 12 to contact the fixedelectrode 14 when inertial force is applied to the inertial weight 8from an unexpected direction.

[0068] (6) The lower surface of each flexible plate is flush with thelower surface of the inertial weight 8 at substantially the middle ofone side of the inertial weight 8. Accordingly, even if the inertialweight 8 pivots in a twisted state, the movable electrodes each contactthe fixed electrode 14.

[0069] It should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention.

[0070] As shown in FIG. 12A, the balancer 9 may be omitted. In thiscase, the acceleration switch 1 is miniaturized.

[0071] As shown in FIG. 12B, the beams 10 may be formed such that thebeams 10 support both sides of the inertial weight 8 and the balancer 9,which are integrally formed with each other.

[0072] As shown in FIG. 12C, the beams 10 may be formed to pivotallysupport the side of the inertial weight 8 that is opposite to the side,in which the flexible plates 11 are arranged.

[0073] The flexible plates 11 do not have to have the same thickness asthe beams 10 as long as the flexible plates 11 are at least thinner thanthe inertial weight 8 and elastically flexible.

[0074] The flexible plates 11 do not have to be generally trapezoidaland may be rectangular or rod-like.

[0075] The flexible plates 11 each may be spaced away from each other.

[0076] The flexible plates 11 may entirely be formed from conductivemetal. Further, the entire flexible plate 11 may be formed as a movableelectrode.

1. (Amended) An acceleration switch including a movable portion (M1),which has a movable electrode (12), and a fixed electrode (14), whereinmovement of the movable portion in accordance with application ofacceleration causes the movable electrode to contact the fixedelectrode, the acceleration switch (1) being characterized in that themovable portion includes: an inertial weight(8) moved in accordance withthe application of acceleration; a beam portion(10) for pivotablysupporting the inertial weight; and a plurality of flexible plates (11)that are arranged in the inertial weight, each flexible plate having adistal end in which the movable electrode is located, the flexibleplates being flexed separately from one another, each flexible platebeing formed to become narrower toward its end, and the width of thedistal end of each flexible plate being substantially equal to the widthof the movable electrode.
 2. The acceleration switch according to claim1, characterized in that the movable portion is made of silicon.
 3. Theacceleration switch according to claim 1 or 2, characterized in that theflexible plates are each thinner than the inertial weight.
 4. (Canceled)5. (Amended) The acceleration switch according to claim 1, characterizedin that the flexible plates each have a generally trapezoidal flatsurface.
 6. (Amended) The acceleration switch according to any one ofclaims 1 to 3 and 5, characterized in that the flexible plates arearranged close to each other.
 7. The acceleration switch according toclaim 6, characterized in that the gap between the flexible plates isabout 10 μm to 200 μm.
 8. The acceleration switch according to claim 7,characterized in that the gap between the flexible plates is about 40μm.
 9. (Amended) The acceleration switch according to any one of claims1 to 3 and 5 to 8, characterized in that the thickness of the flexibleplates is substantially equal to the thickness of the beam portion.